3 DBIx::Class::Manual::FAQ - Frequently Asked Questions (in theory)
7 This document is intended as an anti-map of the documentation. If you
8 know what you want to do, but not how to do it in L<DBIx::Class>, then
9 look here. It does B<not> contain much code or examples, it just gives
10 explanations and pointers to the correct pieces of documentation to
17 =head2 Getting started
21 =item .. create a database to use?
23 First, choose a database. For testing/experimenting, we reccommend
24 L<DBD::SQLite>, which is a self-contained small database (i.e. all you
25 need to do is to install L<DBD::SQLite> from CPAN, and it's usable).
27 Next, spend some time defining which data you need to store, and how
28 it relates to the other data you have. For some help on normalisation,
29 go to L<http://b62.tripod.com/doc/dbbase.htm>.
31 Now, decide whether you want to have the database itself be the
32 definitive source of information about the data layout, or your
33 DBIx::Class schema. If it's the former, look up the documentation for
34 your database, eg. L<http://sqlite.org/lang_createtable.html>, on how
35 to create tables, and start creating them. For a nice universal
36 interface to your database, you can try L<DBI::Shell>. If you decided
37 on the latter choice, read the FAQ on setting up your classes
38 manually, and the one on creating tables from your schema.
40 =item .. use DBIx::Class with L<Catalyst>?
42 Install L<Catalyst::Model::DBIC::Schema> from CPAN. See its
43 documentation, or below, for further details.
45 =item .. set up my DBIx::Class classes automatically from my database?
47 Install L<DBIx::Class::Schema::Loader> from CPAN, and read its documentation.
49 =item .. set up my DBIx::Class classes manually?
51 Look at the L<DBIx::Class::Manual::Example> and come back here if you get lost.
53 =item .. create my database tables from my DBIx::Class schema?
55 Create your classes manually, as above. Write a script that calls
56 L<DBIx::Class::Schema/deploy>. See there for details, or the
57 L<DBIx::Class::Manual::Cookbook>.
59 =item .. connect to my database?
61 Once you have created all the appropriate table/source classes, and an
62 overall L<Schema|DBIx::Class::Schema> class, you can start using
63 them in an application. To do this, you need to create a central
64 Schema object, which is used to access all the data in the various
65 tables. See L<DBIx::Class::Schema/connect> for details. The actual
66 connection does not happen until you actually request data, so don't
67 be alarmed if the error from incorrect connection details happens a
70 =item .. use DBIx::Class across multiple databases?
72 If your database server allows you to run querys across multiple
73 databases at once, then so can DBIx::Class. All you need to do is make
74 sure you write the database name as part of the
75 L<DBIx::Class::ResultSource/table> call. Eg:
77 __PACKAGE__->table('mydb.mytablename');
79 And load all the Result classes for both / all databases using one
80 L<DBIx::Class::Schema/load_namespaces> call.
82 =item .. use DBIx::Class across PostgreSQL/DB2/Oracle schemas?
84 Add the name of the schema to the L<DBIx::Class::ResultSource/table>
85 as part of the name, and make sure you give the one user you are going
86 to connect with rights to read/write all the schemas/tables as
95 =item .. tell DBIx::Class about relationships between my tables?
97 There are a variety of relationship types that come pre-defined for
98 you to use. These are all listed in L<DBIx::Class::Relationship>. If
99 you need a non-standard type, or more information, look in
100 L<DBIx::Class::Relationship::Base>.
102 =item .. define a one-to-many relationship?
104 This is called a C<has_many> relationship on the one side, and a
105 C<belongs_to> relationship on the many side. Currently these need to
106 be set up individually on each side. See L<DBIx::Class::Relationship>
109 =item .. define a relationship where this table contains another table's primary key? (foreign key)
111 Create a C<belongs_to> relationship for the field containing the
112 foreign key. See L<DBIx::Class::Relationship/belongs_to>.
114 =item .. define a foreign key relationship where the key field may contain NULL?
116 Just create a C<belongs_to> relationship, as above. If the column is
117 NULL then the inflation to the foreign object will not happen. This
118 has a side effect of not always fetching all the relevant data, if you
119 use a nullable foreign-key relationship in a JOIN, then you probably
120 want to set the C<join_type> to C<left>.
122 =item .. define a relationship where the key consists of more than one column?
124 Instead of supplying a single column name, all relationship types also
125 allow you to supply a hashref containing the condition across which
126 the tables are to be joined. The condition may contain as many fields
127 as you like. See L<DBIx::Class::Relationship::Base>.
129 =item .. define a relatiopnship across an intermediate table? (many-to-many)
131 Read the documentation on L<DBIx::Class::Relationship/many_to_many>.
133 =item .. stop DBIx::Class from attempting to cascade deletes on my has_many and might_have relationships?
135 By default, DBIx::Class cascades deletes and updates across
136 C<has_many> and C<might_have> relationships. You can disable this
137 behaviour on a per-relationship basis by supplying
138 C<< cascade_delete => 0 >> in the relationship attributes.
140 The cascaded operations are performed after the requested delete or
141 update, so if your database has a constraint on the relationship, it
142 will have deleted/updated the related records or raised an exception
143 before DBIx::Class gets to perform the cascaded operation.
145 See L<DBIx::Class::Relationship>.
147 =item .. use a relationship?
149 Use its name. An accessor is created using the name. See examples in
150 L<DBIx::Class::Manual::Cookbook/Using relationships>.
158 =item .. search for data?
160 Create a C<$schema> object, as mentioned above in ".. connect to my
161 database". Find the L<ResultSet|DBIx::Class::Manual::Glossary/ResultSet>
162 that you want to search in, and call C<search> on it. See
163 L<DBIx::Class::ResultSet/search>.
165 =item .. search using database functions?
167 Supplying something like:
169 ->search({'mydatefield' => 'now()'})
171 to search, will probably not do what you expect. It will quote the
172 text "now()", instead of trying to call the function. To provide
173 literal, unquoted text you need to pass in a scalar reference, like
176 ->search({'mydatefield' => \'now()'})
178 =item .. sort the results of my search?
180 Supply a list of columns you want to sort by to the C<order_by>
181 attribute. See L<DBIx::Class::ResultSet/order_by>.
183 =item .. sort my results based on fields I've aliased using C<as>?
185 You don't. You'll need to supply the same functions/expressions to
186 C<order_by>, as you did to C<select>.
188 To get "fieldname AS alias" in your SQL, you'll need to supply a
189 literal chunk of SQL in your C<select> attribute, such as:
191 ->search({}, { select => [ \'now() AS currenttime'] })
193 Then you can use the alias in your C<order_by> attribute.
195 =item .. group the results of my search?
197 Supply a list of columns you want to group on, to the C<group_by>
198 attribute, see L<DBIx::Class::ResultSet/group_by>.
200 =item .. group my results based on fields I've aliased using C<as>?
202 You don't. You'll need to supply the same functions/expressions to
203 C<group_by>, as you did to C<select>.
205 To get "fieldname AS alias" in your SQL, you'll need to supply a
206 literal chunk of SQL in your C<select> attribute, such as:
208 ->search({}, { select => [ \'now() AS currenttime'] })
210 Then you can use the alias in your C<group_by> attribute.
212 =item .. filter the results of my search?
214 The first argument to C<search> is a hashref of accessor names and
215 values to filter them by, for example:
217 ->search({'created_time' => { '>=', '2006-06-01 00:00:00' } })
219 Note that to use a function here you need to make it a scalar
222 ->search({'created_time' => { '>=', \'yesterday()' } })
224 =item .. search in several tables simultaneously?
226 To search in two related tables, you first need to set up appropriate
227 relationships between their respective classes. When searching you
228 then supply the name of the relationship to the C<join> attribute in
229 your search, for example when searching in the Books table for all the
230 books by the author "Fred Bloggs":
232 ->search({'authors.name' => 'Fred Bloggs'}, { join => 'authors' })
234 The type of join created in your SQL depends on the type of
235 relationship between the two tables, see L<DBIx::Class::Relationship>
236 for the join used by each relationship.
238 =item .. create joins with conditions other than column equality?
240 Currently, L<DBIx::Class> can only create join conditions using
241 equality, so you're probably better off creating a C<view> in your
242 database, and using that as your source. A C<view> is a stored SQL
243 query, which can be accessed similarly to a table, see your database
244 documentation for details.
246 =item .. search with an SQL function on the left hand side?
248 To use an SQL function on the left hand side of a comparison:
250 ->search({ -nest => \[ 'YEAR(date_of_birth) = ?', [ plain_value => 1979 ] ] });
252 Note: the C<plain_value> string in the C<< [ plain_value => 1979 ] >> part
253 should be either the same as the name of the column (do this if the type of the
254 return value of the function is the same as the type of the column) or
255 otherwise it's essentially a dummy string currently (use C<plain_value> as a
256 habit). It is used by L<DBIx::Class> to handle special column types.
258 Or, if you have quoting off:
260 ->search({ 'YEAR(date_of_birth)' => 1979 });
262 =item .. find more help on constructing searches?
264 Behind the scenes, DBIx::Class uses L<SQL::Abstract> to help construct
265 its SQL searches. So if you fail to find help in the
266 L<DBIx::Class::Manual::Cookbook>, try looking in the SQL::Abstract
269 =item .. make searches in Oracle (10gR2 and newer) case-insensitive?
271 To make Oracle behave like most RDBMS use on_connect_do to issue
272 alter session statements on database connection establishment:
274 ->on_connect_do("ALTER SESSION SET NLS_COMP = 'LINGUISTIC'");
275 ->on_connect_do("ALTER SESSION SET NLS_SORT = '<NLS>_CI'");
277 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'BINARY_CI'");
278 ->on_connect_do("ALTER SESSION SET NLS_SORT = 'GERMAN_CI'");
287 =item .. fetch as much data as possible in as few select calls as possible?
289 See the prefetch examples in the L<Cookbook|DBIx::Class::Manual::Cookbook>.
291 =item .. fetch a whole column of data instead of a row?
293 Call C<get_column> on a L<DBIx::Class::ResultSet>. This returns a
294 L<DBIx::Class::ResultSetColumn>. See its documentation and the
295 L<Cookbook|DBIx::Class::Manual::Cookbook> for details.
297 =item .. fetch a formatted column?
299 In your table schema class, create a "private" column accessor with:
301 __PACKAGE__->add_columns(my_column => { accessor => '_hidden_my_column' });
303 Then, in the same class, implement a subroutine called "my_column" that
304 fetches the real value and does the formatting you want.
306 See the Cookbook for more details.
308 =item .. fetch a single (or topmost) row?
310 See L<DBIx::Class::Manual::Cookbook/Retrieve_one_and_only_one_row_from_a_resultset>.
312 A less readable way is to ask a regular search to return 1 row, using
313 L<DBIx::Class::ResultSet/slice>:
315 ->search->(undef, { order_by => "id DESC" })->slice(0)
317 which (if supported by the database) will use LIMIT/OFFSET to hint to the
318 database that we really only need one row. This can result in a significant
319 speed improvement. The method using L<DBIx::Class::ResultSet/single> mentioned
320 in the cookbook can do the same if you pass a C<rows> attribute to the search.
322 =item .. refresh a row from storage?
324 Use L<DBIx::Class::PK/discard_changes>.
326 $row->discard_changes
328 Discarding changes and refreshing from storage are two sides fo the same coin. When you
329 want to discard your local changes, just re-fetch the row from storage. When you want
330 to get a new, fresh copy of the row, just re-fetch the row from storage.
331 L<DBIx::Class::PK/discard_changes> does just that by re-fetching the row from storage
332 using the row's primary key.
334 =item .. fetch my data a "page" at a time?
336 Pass the C<rows> and C<page> attributes to your search, eg:
338 ->search({}, { rows => 10, page => 1});
340 =item .. get a count of all rows even when paging?
342 Call C<pager> on the paged resultset, it will return a L<Data::Page>
343 object. Calling C<total_entries> on the pager will return the correct
346 C<count> on the resultset will only return the total number in the page.
350 =head2 Inserting and updating data
354 =item .. insert a row with an auto incrementing primary key?
356 In versions of L<DBIx::Class> less than 0.07, you need to ensure your
357 table class loads the L<PK::Auto|DBIx::Class::PK::Auto>
358 component. This will attempt to fetch the value of your primary key
359 from the database after the insert has happened, and store it in the
360 created object. In versions 0.07 and above, this component is
361 automatically loaded.
363 =item .. insert a row with a primary key that uses a sequence?
365 You need to create a trigger in your database that updates your
366 primary key field from the sequence. To help PK::Auto find your
367 inserted key, you can tell it the name of the sequence in the
368 C<column_info> supplied with C<add_columns>.
370 ->add_columns({ id => { sequence => 'mysequence', auto_nextval => 1 } });
372 =item .. insert many rows of data efficiently?
374 The C<populate> method in L<DBIx::Class::ResultSet> provides
375 efficient bulk inserts.
377 =item .. update a collection of rows at the same time?
379 Create a resultset using a search, to filter the rows of data you
380 would like to update, then call update on the resultset to change all
383 =item .. use database functions when updating rows?
385 =item .. update a column using data from another column?
387 To stop the column name from being quoted, you'll need to supply a
390 ->update({ somecolumn => \'othercolumn' })
392 But note that when using a scalar reference the column in the database
393 will be updated but when you read the value from the object with e.g.
397 you still get back the scalar reference to the string, B<not> the new
398 value in the database. To get that you must refresh the row from storage
399 using C<discard_changes()>. Or chain your function calls like this:
401 ->update->discard_changes
403 to update the database and refresh the object in one step.
405 =item .. store JSON/YAML in a column and have it deflate/inflate automatically?
407 You can use L<DBIx::Class::InflateColumn> to accomplish YAML/JSON storage transparently.
409 If you want to use JSON, then in your table schema class, do the following:
413 __PACKAGE__->add_columns(qw/ ... my_column ../)
414 __PACKAGE__->inflate_column('my_column', {
415 inflate => sub { jsonToObj(shift) },
416 deflate => sub { objToJson(shift) },
419 For YAML, in your table schema class, do the following:
423 __PACKAGE__->add_columns(qw/ ... my_column ../)
424 __PACKAGE__->inflate_column('my_column', {
425 inflate => sub { YAML::Load(shift) },
426 deflate => sub { YAML::Dump(shift) },
429 This technique is an easy way to store supplemental unstructured data in a table. Be
430 careful not to overuse this capability, however. If you find yourself depending more
431 and more on some data within the inflated column, then it may be time to factor that
436 =head2 Custom methods in Result classes
438 You can add custom methods that do arbitrary things, even to unrelated tables.
439 For example, to provide a C<< $book->foo() >> method which searches the
440 cd table, you'd could add this to Book.pm:
443 my ($self, $col_data) = @_;
444 return $self->result_source->schema->resultset('cd')->search($col_data);
447 And invoke that on any Book Result object like so:
449 my $rs = $book->foo({ title => 'Down to Earth' });
451 When two tables ARE related, L<DBIx::Class::Relationship::Base> provides many
452 methods to find or create data in related tables for you. But if you want to
453 write your own methods, you can.
455 For example, to provide a C<< $book->foo() >> method to manually implement
456 what create_related() from L<DBIx::Class::Relationship::Base> does, you could
460 my ($self, $relname, $col_data) = @_;
461 return $self->related_resultset($relname)->create($col_data);
466 my $author = $book->foo('author', { name => 'Fred' });
472 =item How do I store my own (non-db) data in my DBIx::Class objects?
474 You can add your own data accessors to your classes.
476 One method is to use the built in mk_group_accessors (via L<Class::Accessor::Grouped>)
480 use parent 'DBIx::Class';
482 __PACKAGE__->table('foo'); #etc
483 __PACKAGE__->mk_group_accessors('simple' => qw/non_column_data/); # must use simple group
485 An another method is to use L<Moose> with your L<DBIx::Class> package.
489 use Moose; # import Moose
490 use Moose::Util::TypeConstraint; # import Moose accessor type constraints
492 extends 'DBIx::Class'; # Moose changes the way we define our parent (base) package
494 has 'non_column_data' => ( is => 'rw', isa => 'Str' ); # define a simple attribute
496 __PACKAGE__->table('foo'); # etc
498 With either of these methods the resulting use of the accesssor would be
502 # assume that somewhere in here $row will get assigned to a MyTable row
504 $row->non_column_data('some string'); # would set the non_column_data accessor
506 # some other stuff happens here
508 $row->update(); # would not inline the non_column_data accessor into the update
511 =item How do I use DBIx::Class objects in my TT templates?
513 Like normal objects, mostly. However you need to watch out for TT
514 calling methods in list context. When calling relationship accessors
515 you will not get resultsets, but a list of all the related objects.
517 Starting with version 0.07, you can use L<DBIx::Class::ResultSet/search_rs>
518 to work around this issue.
520 =item See the SQL statements my code is producing?
522 Turn on debugging! See L<DBIx::Class::Storage> for details of how
523 to turn on debugging in the environment, pass your own filehandle to
524 save debug to, or create your own callback.
526 =item Why didn't my search run any SQL?
528 L<DBIx::Class> runs the actual SQL statement as late as possible, thus
529 if you create a resultset using C<search> in scalar context, no query
530 is executed. You can create further resultset refinements by calling
531 search again or relationship accessors. The SQL query is only run when
532 you ask the resultset for an actual row object.
534 =item How do I deal with tables that lack a primary key?
536 If your table lacks a primary key, DBIx::Class can't work out which row
537 it should operate on, for example to delete or update. However, a
538 UNIQUE constraint on one or more columns allows DBIx::Class to uniquely
539 identify the row, so you can tell L<DBIx::Class::ResultSource> these
540 columns act as a primary key, even if they don't from the database's
543 $resultset->set_primary_key(@column);
545 =item How do I make my program start faster?
547 Look at the tips in L<DBIx::Class::Manual::Cookbook/"STARTUP SPEED">
549 =item How do I reduce the overhead of database queries?
551 You can reduce the overhead of object creation within L<DBIx::Class>
552 using the tips in L<DBIx::Class::Manual::Cookbook/"Skip row object creation for faster results">
553 and L<DBIx::Class::Manual::Cookbook/"Get raw data for blindingly fast results">
555 =item How do I override a run time method (e.g. a relationship accessor)?
557 If you need access to the original accessor, then you must "wrap around" the original method.
558 You can do that either with L<Moose::Manual::MethodModifiers> or L<Class::Method::Modifiers>.
559 The code example works for both modules:
561 package Your::Schema::Group;
562 use Class::Method::Modifiers;
564 # ... declare columns ...
566 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
567 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
569 # if the server group is a "super group", then return all servers
570 # otherwise return only servers that belongs to the given group
571 around 'servers' => sub {
575 return $self->$orig(@_) unless $self->is_super_group;
576 return $self->result_source->schema->resultset('Server')->all;
579 If you just want to override the original method, and don't care about the data
580 from the original accessor, then you have two options. Either use
581 L<Method::Signatures::Simple> that does most of the work for you, or do
584 L<Method::Signatures::Simple> way:
586 package Your::Schema::Group;
587 use Method::Signatures::Simple;
589 # ... declare columns ...
591 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
592 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
594 # The method keyword automatically injects the annoying my $self = shift; for you.
596 return $self->result_source->schema->resultset('Server')->search({ ... });
601 package Your::Schema::Group;
604 # ... declare columns ...
606 __PACKAGE__->has_many('group_servers', 'Your::Schema::GroupServer', 'group_id');
607 __PACKAGE__->many_to_many('servers', 'group_servers', 'server');
609 *servers = subname servers => sub {
611 return $self->result_source->schema->resultset('Server')->search({ ... });
616 =head2 Notes for CDBI users
620 =item Is there a way to make an object auto-stringify itself as a
621 particular column or group of columns (a-la cdbi Stringfy column
622 group, or stringify_self method) ?
624 See L<DBIx::Class::Manual::Cookbook/Stringification>
628 =head2 Troubleshooting
632 =item Help, I can't connect to postgresql!
634 If you get an error such as:
636 DBI connect('dbname=dbic','user',...) failed: could not connect to server:
637 No such file or directory Is the server running locally and accepting
638 connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
640 Likely you have/had two copies of postgresql installed simultaneously, the
641 second one will use a default port of 5433, while L<DBD::Pg> is compiled with a
642 default port of 5432.
644 You can change the port setting in C<postgresql.conf>.
646 =item I've lost or forgotten my mysql password
648 Stop mysqld and restart it with the --skip-grant-tables option.
650 Issue the following statements in the mysql client.
652 UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
659 L<http://dev.mysql.com/doc/refman/5.1/en/resetting-permissions.html>.